1. Field of the Invention
This invention relates generally to a process of making an instant coffee, particularly a spray-dried instant coffee, which, when contacted with hot water, produces a foam which simulates the foam formed on espresso made from roasted and ground espresso coffee. More specifically, the present invention is directed to a process for making a soluble espresso coffee powder which results in an instant espresso product having significantly improved foam texture and stability compared to that produced by soluble espresso products currently available to the consumer. Dependent upon the steps used to gasify and dry the coffee extract, the resulting soluble espresso coffee powder produced by the process of the present invention has incorporated in its structure gas bubbles a majority of which are less than ten microns. The minute size of these gas bubbles is essential to the delivery of the improved in-cup foam.
2. Description of the Prior Art
The worldwide popularity and growing consumption of coffee has made it one of the leading agricultural products in international trade along with wheat, soybeans and corn. The coffee beverage itself comprises an aqueous solution of the mostly water-soluble constituents of the roasted and ground beans of the coffee plant, belonging to the family Rubiaceae. Although many species of the coffee plant exist, it is Coffea arabica and Coffea robusta which account for roughly 99% of the world production. Other species, such as Coffea liberica, make up the remaining 1%. Each species includes several varieties, and each variety can have different characteristic flavors dependent upon the area and conditions in which it is grown. Many times commercial roasters will blend or mix varieties to obtain a preferred flavor. Consequently, there exist many varying types of coffee.
Most generally, the coffee extract is brewed by contacting the roasted and ground coffee with boiling or near-boiling water for a predetermined brewing time. The extract, including the solutes, is then separated from the insolubles to obtain the resulting beverage which is promptly consumed. However, in this day and age where there is a significant trend towards convenience foods, the use of instant coffees is preferred by a segment of coffee consumers.
Instant coffee is basically the dried water-extract of roasted, ground coffee. The beans used to make instant coffee are blended, roasted and ground as they are in the making of regular coffee. In order to make instant coffee, the roasted, ground coffee is then charged into columns called percolators through which hot water is pumped, resulting in a concentrated coffee extract. The extract is then dried, usually by either spray drying or freeze drying, to produce the final coffee powder which is sold to the consumer. Upon the simple addition of hot water to the dried coffee powder, coffee is obtained without the need to go through the usual and more complicated brewing steps.
As is explained in Canadian Pat. No. 670,794 (to Standard Brands Incorporated), spray dried instant coffee consists of hollow spheres or aggregates thereof which form a fine and persistent foam when hot water is added to the coffee powder. This is in contrast to the coarser and more quickly subsiding foam which is formed when a hot water extract of ground roasted coffee is poured into a cup. Consequently, because typically brewed coffee does not have such a foam, the foam produced by the spray dried instant coffee is undesirable. Accordingly, many techniques have been developed to reduce, alter or eliminate the foaming characteristics of spray dried instant coffee. For example, in Canadian Pat. No. 690,794, a small amount of a monoglyceride of a higher fatty acid is incorporated in the spray dried coffee to change the appearance of the foam produced when the coffee is contacted with hot water. The new foam has the characteristics of the foam in a cup of brewed coffee rather than the more persistent fine foam normally associated with spray dried instant coffee.
On the other hand, the production of foam on coffee is not always undesirable. In particular, espresso coffee is a special coffee beverage type that is winning increased approval with the consumer. Espresso coffee typically comprises finely milled dark roasted beans which are brewed rapidly with pressurized water/steam which coincidentally results in the formation of in-cup foam. The resulting espresso beverage provides body and flavor aspects very distinct from the normal cup of coffee. Espresso is said to have a dark, rich flavor and appearance and is accompanied by a head of lighter-colored froth or foam which espresso beverage devotees consider crucial. The foam contains colloidal oil droplets and solid particles which give the espresso its characteristic texture and mouthfeel. It is to be noted that the froth or foam characteristic of espresso coffee is not at all similar to the foam formed from the spray dried instant coffee described above.
As would be expected, due to its unique flavor and other characteristics, espresso coffee is not easily made. In order to produce a consistently high-quality espresso beverage, the brewing process must be controlled very closely, i.e. a very short brewing time, specific pressures, temperatures, volumes of water delivered to the grinds, the need for precise adjustments, etc. Consequently, espresso brewing machines are relatively complicated, large and expensive and require a certain amount of skill to operate. Accordingly, it would be preferable to find an alternative method for providing an espresso beverage, one which is simpler and easier to employ.
Although the flavor of espresso coffee may be mimicked by the use of dark roast Arabicas and extraction processing conditions, the foaming characteristics of espresso are not easily replicated as the foaming of roasted and ground espresso is primarily induced by high pressure steam which is provided by the Espresso machine. The high pressure steam provides a source of sparging gas, which, with the aid of surface active species present in the coffee, form foam cells. Espresso brewing also results in the emulsification of oil into the brew and the foam. The resultant foam consists of water, gas, surface active species and oil, and has a creamy appearance and texture.
U.S. Pat. Nos. 4,830,869 and 4,903,585, both to Wimmers et al., disclose a method for making a coffee beverage having a thick layer of foamed coffee on its surface, similar in appearance to cappuccino coffee. A measured amount of spray dried instant coffee and a small amount of cold water are combined with vigorous agitation to form a foamed coffee concentrate. Then, hot water is added to make a coffee beverage.
U.S. Pat. No. 4,618,500 to Forquer discloses a method for preparing a brewed espresso-type coffee beverage which has a head of froth on the surface of the beverage. Relatively dry steam is injected into the brewed coffee beverage to produce the froth.
U.S. Pat. No. 3,749,378 to Rhodes discloses an apparatus for foaming a coffee extract. Gas is introduced into the coffee extract and the foamed coffee is then spray-dried to make a soluble coffee product having a low bulk density.
Accordingly, in response to the increasing consumer interest in premium and specialty coffees, a soluble espresso coffee would be of interest to consumers if it could deliver the distinctive espresso product attributes without the need for an Espresso machine, or the special requirements of the patents noted above, and with all the convenience and benefits of soluble coffee.
For a soluble coffee product, no chemical or mechanical method of creating foam is possible during product make-up, thus the product must be processed from a foam state prior to drying, and be capable of recovering this state when prepared for consumption.
A foamed coffee extract, if dried properly, will contain small gas bubbles in the walls of the spray dried particles. When hot water is poured on these particles, the gas bubbles will be released as the coffee dissolves, and the bubbles will float to the surface of the beverage. If sufficient surface active agents are present in the brew, the bubbles will be stabilized by the adsorption of these compounds at the gas bubble/water interface, and will be trapped as a foam layer on the surface.
Although some soluble espresso coffee powders are available in the market, they do not provide the foam characteristics desired by the true espresso connoisseur. Generally, the resulting espresso beverage lacks sufficient foam, the foam dissipates too quickly or there is a combination of both. Accordingly, a soluble espresso coffee is desirable which provides foam characteristics of a conventionally made espresso beverage.